Extruded evaporator drain pan

ABSTRACT

A drain pain is disclosed. The drain pain includes a base sheet, an extruded covering sheet coupled to the base sheet, the extrusion defining a tube cavity having a heat transfer surface, and a heat tube inserted into the tube cavity. The tube cavity has dimension such that the heat transfer surface is in contact with the heat tube.

This application claims the benefit of U.S. Provisional Application No. 61/360,006 filed Jun. 30, 2010, the entire content of which is incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to an evaporator drain pan, particularly for use in a defrost cycle in a refrigeration system.

BACKGROUND OF THE INVENTION

Refrigeration systems affect our lives in many ways. For example, refrigerators keep our food from spoiling, freezers prevent ice cream from melting, and air conditioners create comfortable living space even in the hottest weather. It is hard to imagine a world before the invention of refrigeration systems.

A typical refrigeration system includes a compressor 10, a condensor 12, an expansion valve 14 and an evaporator 16, with a refrigerant circulating through these components as shown in FIG. 1. The evaporator 16 includes evaporator coils 18 and drain pan 20. The refrigerant is a liquid that has a low boiling point, which is used to absorb heat as it evaporates, thereby, making the surrounding environment colder. When the refrigerant enters the compressor 10, the temperature of the refrigerant rises as the surrounding pressure is increased. The hot refrigerant gas then passes through the condensor 12 where it dissipates heat, turning into a liquid. As the high pressure liquid refrigerant passes through the expansion valve 14, the temperature is dropped because of the drop in pressure, and when it enters the evaporator coils 18 in the evaporator 16, the surrounding warmer environment causes the refrigerant (with a low boiling point) to boil and evaporate. During evaporation, the refrigerant absorbs heat from the surrounding environment.

However, as the evaporator coils 18 cool, frost forms on the surface. Many have witnessed this in older refrigerators with freezers where frost build up eventually rendered the freezer useless. As such, modern refrigerators have a defrost cycle in addition to the refrigeration cycle to ensure that frost does not accumulate. Generally speaking, defrost cycle applies heat to the evaporator coils 18 at a predetermined time in-between refrigeration cycles to remove any frost from building up on the evaporator coils 18. This can be achieved either by activating heating coils or by applying hot gas. The former entails turning on heating coils (embedded in-between the evaporator coils 18) in the evaporator 16 to melt away any frost build-up, while the latter involves redirecting the hot refrigerant gas from the compressor 10 into the evaporator coils 18 in the evaporator 16. While heating coils defrost the evaporator coils 18 faster than hot gas defrost systems, it is less energy efficient and more expensive to implement.

Similarly to evaporator coils 18, drain pan 20 may also be defrosted using heat coils rather than hot gas. However, while defrost time is reduced, such defrost systems suffer from the same disadvantages as discussed above.

Hot gas defrost systems can be generally divided into two types of systems: reverse cycle defrost (FIG. 2) and 3-pipes defrost (FIG. 3). In the reverse cycle defrost system, the path of the refrigerant is reversed such that the hot refrigerant gas exiting the compressor 10 is pumped directly into the drain pan 20 and evaporator coils 18 via hot gas line 22 without first passing through the condensor 12 and expansion valve 14. During this process, the hot refrigerant gas removes any frost build-up in the drain pan 20 and on the evaporator coils 18. The refrigerant, which is now a liquid, flows out of the evaporator coils 18 and into the distributor 24. During the reverse cycle, the check valve 26 is open so that the refrigerant bypasses the expansion valve 14. The refrigerant then loops back to the other evaporators to be re-evaporated.

As for the 3-pipes defrost system, the hot refrigerant gas from the compressor 10 is redirected to the hot gas line 22 of the evaporator 16. In the evaporator 16, the hot gas flows through the drain pan 20 to remove any frost build-up and then bypasses expansion valve 14 by flowing through the check valve 26. The hot gas then flows through the distributor 24 and into the evaporator coils 18 to remove any frost build-up. The refrigerant, which is now a liquid, is pumped out of the evaporator coils 18 by the suction line 23. The refrigerant eventually makes its way back to the compressor 10.

A typical drain pan 20 using hot gas defrosting system is shown in FIG. 4. As shown, heat tubes 30, carrying hot refrigerant gas, are inserted between the top and bottom metal sheets 32, 34 of the drain pan 20. Along with the heat tubes 30, there is a layer of insulation 36 to ensure that the heat from the heat tubes 30 is not easily dissipated from the drain pan 20. A disadvantage of current drain pan design is that only a small circumference of the heat tube is actually in contact with the top sheet 32 of the drain pan 20. As a result, defrost time for the drain pan 20 is longer than a drain pan using heat coils. Moreover, increased defrost time results in increased dissipation of heat into the surrounding environment, thus resulting in wasted energy. Therefore, there is a need for a drain pan that better transfers heat from the heat tubes into the drain pan.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a drain pan is disclosed. The drain pain includes a base sheet, an extruded covering sheet coupled to the base sheet, the extrusion defining a tube cavity having a heat transfer surface, and a heat tube inserted into the tube cavity. The tube cavity has dimension such that the heat transfer surface is in contact with the heat tube.

In according with a further aspect of the invention, a refrigeration system including a compressor, a condensor, an expansion valve and an evaporator, the evaporator including an evaporator coil and a drain pan, in fluid connection is disclosed. During a refrigeration cycle and a defrost cycle, a refrigerant circulates through the refrigeration system. In the refrigeration system, the drain pan includes a base sheet, an extruded covering sheet, the extrusion defining a tube cavity having a heat transfer surface, and a heat tube inserted into the tube cavity. The tube cavity having dimension such that the heat transfer surface is in contact with the heat tube.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:

FIG. 1 is a block diagram of a typical refrigerant system;

FIG. 2 illustrates the reverse cycle defrost mechanism incorporated in a typical refrigerant system as shown in FIG. 1;

FIG. 3 illustrates the 3-pipes defrost mechanism incorporated in a typical refrigerant system as shown in FIG. 1;

FIG. 4 is a cross-sectional view of a known defrost mechanism incorporated within a drain pan;

FIG. 5 is a perspective view of the drain pan in accordance with an embodiment of the present invention;

FIG. 6 is an exploded view of the drain pan in accordance with an embodiment as shown in FIG. 5;

FIG. 7 is a cross-sectional view of the drain pan as shown in FIG. 5;

FIG. 8 is a detailed cross-sectional view of the drain pan as shown in FIG. 5;

FIG. 9 is a performance graph of the known drain pan as shown in FIG. 4, operating in a defrost cycle; and

FIG. 10 is a performance graph of the drain pan in accordance with an embodiment of the present invention as shown in FIG. 5, operating in a defrost cycle.

DETAILED DESCRIPTION

While the patent disclosure is described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the patent disclosure to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the scope of the patent disclosure as defined by the appended claims. In the description below, numerous specific details are set forth in order to provide a thorough understanding of the present patent disclosure. The present patent disclosure may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail in order not to unnecessarily obscure the present patent disclosure.

In this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs.

It will be further understood that the terms “comprises” or “comprising”, or both when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The details and particulars of these aspects of the present invention will now be described below, by way of example, with reference to the attached drawings.

An embodiment of the present invention is shown in FIGS. 5 and 6. As shown, the drain pan 100 includes an extruded covering sheet 102, 104, a heat tube 106 and a base sheet 110. In this particular embodiment, the extruded covering sheet includes two opposing covering sheets 102, 104 that abut at an edge 130 (see FIG. 8). The drain pan 100 further includes a plurality of heat tubes 106. Additionally, the two opposing covering sheets 102, 104 may be slanted toward the edge of abutment 130 to define a collection area 116 (see FIG. 7). The collection area 116 is area along the slant with the lowest elevation such that when condensation drips into the drain pan 100, liquid condensate is collected starting from the collection area 116. While this particular embodiment is shown to include two opposing extruded covering sheets 102, 104, it is reasonably contemplated that the covering sheet may be extruded as a single sheet or more than two sheets. Moreover, while FIGS. 5 and 6 depict the drain pan 100 with a plurality of heat tubes 106, a person skilled in the art would understand that the drain pan 100 may include a single heat tube 106.

Now referring to FIG. 7, a cross section of the drain pan 100 is shown. As discussed, the extruded covering sheets 102, 104 are angled to converge at the edge of abutment 130 to help contain the collected liquid condensate. In-between the covering sheets 102, 104 and base sheet 110, there may be a layer of insulation foam 108 to help fully harness the heat from the heat tube 106. The heat tube 106 is inserted into the tube cavity 120 (see FIG. 8) created in the extruded covering sheet 102, 104. As it will be described below, because of the extrusion, there is a greater surface area of contact between the heat tube 106 and the extruded covering sheet 102, 104. By comparison, in drain pan 20 shown in FIG. 4, the heat tubes 30 are sandwiched between the insulation layer 36 and the top sheet 32. In effect, only a small surface area of the heat tubes 30 comes into contact with the top sheet 32. While the layer of insulation 36 helps contain the heat dissipated by the heat tubes 30, the defrosting process is much slower than if the heat was directly applied to top sheet 32.

Turning to FIG. 8, the extruded covering sheet 102, 104 will be explained in detail. The covering sheet 102, 104 is extruded to form a tube cavity 120 having a heat transfer surface 121. In this particular embodiment, the tube cavity 120 is circular in cross-section having a diameter and a circumferential edge. The circumferential edge includes the heat transfer surface 121 as shown in FIG. 8.

The tube cavity 120 is dimensioned such that when the heat tube 106 is inserted into the heat cavity 120, the heat transfer surface 121 of the tube cavity 120 is in direct contact with the heat tube 106. Thus, when the hot refrigerant passes through the heat tube 106 during the defrost cycle, heat from the heat tube 106 can be transferred directly to the extruded covering sheet 102, 104. Since the heat transfer surface 121 provides a large surface contact area between the extruded covering sheet 102, 104 and the heat tube 106, the drain pan 100 may be efficiently and quickly defrosted. In one embodiment of the present invention, the diameter of the tube cavity 120 is 0.5 inch. Additionally, to increase the contact between the heat tube 106 and the heat transfer surface 121 of the tube cavity 120, the heat tube may be expanded using an expander to ensure good contact between the heat tube 106 and the heat transfer surface 121.

By contrast, in the drain pan 20 (see FIG. 4), the heat tube 30 has a small surface contact area between the heat tube 30 and the top sheet 32. In the embodiment shown in FIG. 8, the heat tube 106 comprises of 8 heat tubes per extruded covering sheet 102, 104. However, other reasonable configurations are also contemplated in this invention. For example, the heat tube 106 comprising of 6 tubes per extruded covering sheet 102, 104 have been found to be more than adequate in effectively removing frost from the drain pan. In another embodiment of the invention, the heat tube 106 may be made of copper and the extruded covering sheet 102, 104 may be made of aluminum to ensure good heat transfer characteristics.

In a further embodiment of the present invention, additional cavities may be provided. As shown in FIG. 8, the extruded covering sheet 102, 104 may include an inset 122, 124. The inset 122, 124 may be used to save material and reduce weight of the drain pan 100. Additionally, or alternatively, the insets 122, 124 may be used to incorporate heating coils, which may assist in the defrosting process. Furthermore, the tube cavity 120 may include a slit 126 to help the tube cavity 120 expand with the heat tube 106, thereby helping to prevent any cracks from forming during the expansion of the material. With the slit 126, greater expansion of the tube cavity 120 is permitted.

In the particular embodiment shown, the covering sheet is made of two opposing extruded covering sheets 102 and 104. They are mirror images of one another and positioned so that the two opposing extruded covering sheets 102, 104 abut at an edge 130. To securely assemble the two opposing extruded covering sheets 102, 104, they may be welded together upon joining. The opposing covering sheets 102, 104 may also include a chamfer 132, 134 to facilitate welding of the covering sheets 102, 104. The covering sheets 102, 104 and the base sheet 110 may also be welded together.

Alternatively, or additionally, the opposing extruded covering sheets 102, 104, heat tube 106, insulating foam 108 and base sheet 110 may be joined together by a joining cap 112, 114 (see FIG. 6)

The drain pan 100 as discussed above is suitable for any refrigeration system that normally requires a drain pan and that utilizes hot gas as the defrost mechanism. Previous implementations of heat tubes in drain pan (such as those shown in FIG. 4) have always been the bottleneck when defrosting the evaporator 16 using hot gas. In other words, the evaporator coils 18 defrosted quicker than the drain pan 20. However, testing of the evaporator 16 incorporating the drain pan 100, implementing an embodiment of the present invention, has shown a significant improvement in the defrost cycle. This improvement has allowed the drain pan 100 embodying the present invention to defrost faster than the evaporator coils 18 and, thus, it is no longer the performance bottleneck in the defrost cycle.

Referring to FIG. 9, the defrost cycle of a known drain pan, such as drain pan 20 in FIG. 4, is shown. As it can be seen, the defrost cycle (i.e. 202) lasted between 11:30-12:30, a total of 1 hour. During the defrost cycle, the temperature of the drain pan (i.e. 200) rose to well above zero and remained there for the duration of the defrost cycle. While the defrost cycle is activated, heat is expelled into the surrounding environment and the refrigeration system must work harder to remove the heat in the subsequent refrigeration cycle. By contrast, FIG. 10 shows the defrost cycle of the drain pan, such as drain pan 100, in accordance with the present invention. As shown, the defrost cycle (i.e. 206) lasted between 7:15 to 7:23, which is a total of only 7 minutes. Moreover, the temperature of the drain pan (i.e. 204) rose above zero and remained above zero for approximately 10 minutes (i.e. 7:20 to 7:30). Thereafter, the temperature of the drain pan quickly dropped back to sub-zero temperature. This quick transition is attributable to the fact that the defrost cycle of the drain pan, in accordance with the present invention, is significantly shorter than the defrost cycles of previously known drain pans. Thus, the refrigeration system does not need to work as hard to remove the heat that was added to the surrounding environment during the defrost cycle.

One or more currently preferred embodiments have been described by way of example. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention. 

1. A drain pan comprising: a base sheet; an extruded covering sheet coupled to the base sheet, the extrusion defining a tube cavity having a heat transfer surface; and a heat tube inserted into the tube cavity; wherein, the tube cavity having dimension such that the heat transfer surface is in contact with the heat tube.
 2. The drain pan according to claim 1, wherein the extruded covering sheet comprises two opposing covering sheets, the opposing covering sheets abutting at an edge.
 3. The drain pan according to claim 2, wherein each of the opposing covering sheets having a slant toward the edge of abutment to define a collection area, the collection area being the area along the slant having the lowest elevation.
 4. The drain pan according to claim 1, further comprising an insulation foam positioned between the base sheet and the covering sheet.
 5. The drain pan according to claim 1, wherein the extrusion defines a plurality of tube cavities, each of the plurality of tube cavities having a heat transfer surface.
 6. The drain pan according to claim 5, wherein a plurality of heat tubes are inserted into the plurality of tube cavities.
 7. The drain pan according to claim 1, wherein the covering sheet further comprises an inset.
 8. The drain pan according to claim 1, wherein the tube cavity comprises a slit to accommodate the expansion of the heat tube.
 9. The drain pan according to claim 1, wherein the heat tube is made of copper.
 10. The drain pan according to claim 1, wherein the extruded covering sheet is made of aluminium.
 11. The drain pan according to claim 1, wherein the base sheet and the covering sheet are coupled by welding the sheets together.
 12. The drain pan according to claim 1, wherein the base sheet and the covering sheet are coupled together by a joining cap.
 13. The drain pan according to claim 1, wherein the tube cavity is circular in cross-section, the circular cross-section having a diamer and a circumferential edge.
 14. The drain pan according to claim 13, wherein the diameter is approximately 0.5 inch.
 15. The drain pan according to claim 13, wherein the circumferential edge comprises the heat transfer surface.
 16. The drain pan according to claim 1, wherein the heat tube is expanded using an expander for increasing the contact between the heat tube and the heat transfer surface.
 17. A refrigeration system comprising a compressor, a condensor, an expansion valve and an evaporator, the evaporator including an evaporator coil and a drain pan, in fluid connection, a refrigerant circulating through the refrigeration system during a refrigeration cycle and a defrost cycle, the drain pan comprising: a base sheet; an extruded covering sheet, the extrusion defining a tube cavity having a heat transfer surface; and a heat tube inserted into the tube cavity; wherein, the tube cavity having dimension such that the heat transfer surface is in contact with the heat tube.
 18. The refrigeration system according to claim 17, wherein the extrusion defines a plurality of tube cavities, each of the plurality of tube cavities having a heat transfer surface.
 19. The refrigeration system according to claim 18, wherein a plurality of heat tubes are inserted into the plurality of tube cavities. 